Abstract

We previously showed that ethnicity modifies the association between adiposity and insulin resistance. We sought to determine whether differential body fat partitioning or abnormalities in muscle insulin signaling associated with higher levels of adiposity might underlie this observation. We measured insulin sensitivity index (ISI), %body fat, visceral (VAT) and subcutaneous (SAT) adipose tissue, liver fat and intramyocellular lipids (IMCL) in 101 Chinese, 82 Malays and 81 South Asians as well as p-Akt levels in cultured myoblasts from Chinese and South Asians. Lean Chinese and Malays had higher ISI than South Asians. Although ISI was lower in all ethnic groups when %body fat was higher, this association was stronger in Chinese and Malays such that, in overweight individuals, no ethnic differences were observed. These ethnic differences were observed even when %body fat was replaced with fat in other depots. Myoblasts obtained from lean South Asians had lower p-Akt levels than those from lean Chinese. Higher adiposity was associated with lower p-Akt levels in Chinese but not in South Asians, and no ethnic differences were observed in overweight individuals. With higher %body fat, Chinese exhibited smaller increases in DSAT and IMCL compared to Malays and South Asians, which did not explain the ethnic differences observed. Our study suggests that body fat partitioning does not explain inter-ethnic differences in insulin sensitivity among Asian ethnic groups. While higher adiposity had greater impact on skeletal muscle insulin sensitivity among Chinese, obesity-independent pathway may be more relevant in South Asians.